Respective members such as electric wires, wire harnesses and pipes, which are arranged in automobiles, aerospace equipments or the like, are used under a high-temperature environment, so that adhesive materials used in protection, connection, hermetic sealing or the like thereof are required to have high heat resistance that a continuous service temperature is at least 150° C.
For example, a heat-shrinkable tube, on the internal surface of which a hot-melt adhesive layer has been arranged, is used in binding and connection of wire harnesses used in an automobile, or protection of a branched portion from the viewpoints of insulating property and waterproofness. The heat-shrinkable tube, on the internal surface of which the hot-melt adhesive layer has been arranged, is also used for improving the anticorrosion of a hydraulic piping composed of copper, iron, stainless steel or the like and the waterproofness of a joint.
In the heat-shrinkable tube, on the internal surface of which the hot-melt adhesive layer has been arranged, the hot-melt adhesive is melted to be filled in a space between the surface of an adherend and the heat-shrinkable tube and bonded to the adherend when the heat-shrinkable tube is heated and shrunk to bring it into close contact with the periphery of the adherend, whereby penetration of water and corrosive gases from an end of the heat-shrinkable tube is prevented, thereby exhibiting waterproofness and anticorrosion.
As a material for forming a heat-shrinkable tube body, has heretofore been used, for example, polystyrene, polyvinyl chloride, crosslinked polyethylene, fluororesin or fluororubber. A heat-shrinkable tube composed of a fluorine-containing polymer such as a fluororesin or fluororubber is generally used in uses of which high heat resistance that a continuous service temperature is at least 150° C. is required.
Adhesive compositions comprising, as a principal component, a polyamide resin such as a dimer acid type polyamide resin, polyamide 6, polyamide 10 or polyamide 11 are representative of the hot-melt adhesive arranged on the internal surface of the heat-shrinkable tube. These hot-melt adhesives are coated on the internal surface of the heat-shrinkable tube. However, the continuous service temperature of these hot-melt adhesives is at most about 105° C., so that they cannot be applied to uses of which high heat resistance that a continuous service temperature is at least 150 is required. In other words, when a conventional heat-shrinkable tube is held for along period of time under high-temperature conditions of at least 150° C. in a state that it has been brought into close contact with the periphery of an adherend, its adhesion strength to the adherend is lowered.
There has heretofore been proposed a heat-shrinkable tube of a 2-layer structure that a layer of a fluororesin composition having a low melting point and high flowability is arranged on an internal surface of a crosslinked heat-shrinkable tube composed of a fluororesin (Japanese Patent Application Laid-Open No. 5-57791). According to this heat-shrinkable tube, the fluororesin composition of the internal layer can be melted upon the shrinkage under heating to be filled in a space between an adherend and the heat-shrinkable tube. However, the fluororesin composition does not have adhesive property, so that the heat-shrinkable tube may not be satisfactory in that the function of being bonded to the adherend to improve waterproofness and anticorrosion is exhibited.